This invention relates to a recuperator for heat exchange between flow media of dissimilar temperatures, and in a broad aspect it provides a recuperator that is easy to maintain and is configured such that it can still be used when the hotter of the two flow media is at a temperature of at least 1000.degree. C.
It is a particular object of the present invention to provide a recuperator wherein a housing containing the flow of the first of two flow media also has a plurality of essentially parallel tubes containing the flow of the second flow medium arranged therein. According to a preferred embodiment these tubes are made of a highly heat-resistant ceramic material and extend at right angles to the direction of flow of the first flow medium around the tubes for causing a meandering of the second flow medium through the tubes. In a further feature of the invention, at least two tubes at a time are interconnected at adjacent ends by means of a component of a highly heat-resistant material. This component deflects the flow from the one tube into the other tube, and pressure is applied to that surface of the respective component which points away from the tube ends so as to urge the component against the tube ends.
The recuperator of the present invention provides an advantage in that for the tubes, use can be made of high-strength ceramic materials of any coefficient of thermal expansion, in that maintenance is very simple, the various tubes being readily replaced, and in that the use of highly heat-resistant ceramic materials for the tubes enables heat exchange to be achieved between two flow media of temperatures in the 1000.degree. to 1400.degree. C. range.
In a further aspect of the present invention, an expansion mechanism to generate the above-noted pressure, which acts on those surfaces of the components which point away from the tube ends, is provided between a first wall of the housing and the components arranged at the one ends of the tubes, said expansion mechanism operating on the force of a spring or pressure medium that operationally abutts on the one wall of the housing, and acting on the components arranged at the one end of the tubes to urge the components against the one tube ends thereby c using the tubes to press against the components arranged at the other tubes ends, said components in turn abutting on a second, opposite wall of the housing.
As expansion mechanisms, use can be made either of spring-loaded bolts or compressed-air cylinders equally made of highly heat-resistant ceramic materials.
In a further aspect of the present invention a pressure chamber is optionally arranged, in lieu of an expansion mechanism, between the components at the one tube ends and the adjacent wall of the housing, which pressure chamber develops pressure when in operation to act on that surface of the components which points away from the one tube ends to urge the components against the tube ends.
According to a further preferred embodiment, the pressure chamber is defined by a pressurizeable elastic foil of a highly heat resistant material disposed between the components and the wall of the housing.
In a further aspect of the present invention each of the noted deflecting components has a number of annular slots corresponding to the number of tubes to be interconnected by this component, in which annular slots are inserted the adjacent ends of the tubes to be interconnected by this component.
In a preferred aspect of the present invention a seal is provided in each annular slot between the tube ends inserted into said annular slot and the bottom of the annular slot, where the seal can be either a highly heat-resistant, ceramic or metal felt material.
Another arrangement for connecting the tube ends to the components according to the invention is to make each component snugly fit the contour of the tube ends connected to this component, where each component and the tube ends connected to this component preferably have spherical mating surfaces. This arrangement provides an advantage in that the need for an additional seal between the mating surfaces of the components and tubes is eliminated, in that the recuperator can be assembled at a faster rate, and in that even in the presence of minor rotary movements of the tubes about their ends the sealing effect between the components and the tubes will continue unchanged.
In a still further aspect of the present invention, the tubes are arranged and stacked in layers and the components are a snug fit one with the other, the tubes being spaced apart to permit the flow of the first flow medium between them. In a preferred aspect, the ends of at least two tubes of respective uppermost and lowermost layers of tubes are interconnected by means of an adaptor designed for the ingress and egress of the second flow medium, the components of the respective layer of tubes above and below being snug fit with the adaptors and two adjacent adaptors at a time being urged against the one ends of the tubes connected by said two adaptors by means of one of the expansion mechanisms.
In yet another feature of the present invention, components interconnecting three tubes at a time can be used instead of the noted two tube connecting components, the flow being deflected from one tube into the two others, or from two tubes into the remaining tube. This provides an advantage in that the position of the components is defined statically.
The recuperator of the present invention is suitable especially for use in a vehicular gas turbine engine fitted with a regenerative heat exchanger made of a ceramic material. The recuperator of the present invention is then arranged in the turbine operating cycle such that the hot steam of exhaust gas, when issuing from the turbine, will first flow through the recuperator of the present invention and then through the regenerative heat exchanger.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, plural embodiments in accordance with the present invention.